package chapter04;import java.util.Date;public class oop_test {    public static void main(String[] args) {//        Date deadline;//        deadline = new Date();//        Date birthday = new Date();//        deadline = birthday;//        deadline = null;//        System.out.println("birthday : "+ birthday);//        if(deadline != null)//            System.out.println("deadline : "+ deadline);//        StringBuilder sb = new StringBuilder("abc");//        AA a = new AA(sb);////        System.out.println(a.getName());//        a.setName("def");//        System.out.println(a.getName());        AA a = new AA(20);        System.out.println("main:" + a.getAge());        setage(a);        System.out.println("main:" + a.getAge());    }    public static void setage(AA a)    {        System.out.println("setage:" + a.getAge());        a.setAge(2000);        System.out.println("setage:" + a.getAge());    }}